Hot, Flat, and Crowded by Thomas L. Friedman: This is the readable bible of the current environmental challenges facing the world and how we can address them.  Friedman does an excellent job of integrating anecdotes to keep the book interesting, while keeping the text highly informative.  He focuses specifically on America -- the reasons for its lack of action and how acting can restore the nation.  The book I always suggest for anyone interested in learning about environmentalism, my Economics class even used it as required reading this summer! (Hardcover at BarnesandNoble.com: new $22; used from $7.55)

The Green Collar Economy by Van Jones: I've quoted Van Jones' book many times in my blogs, mainly because he shows a completely unique side to environmentalism.  Jones describes green solutions in relation to how they can uplift lower-income and middle-class Americans, fostering justice across racial and economic divides.  Plus, it's a quick read, and Jones provides specific policy suggestions, which can be of use to any grassroots activist or elected politician.  As Van Jones is the Energy Czar under Obama, his book gives you the chance to read the same advice the president is receiving! (Hardcover at BarnesandNoble.com: new $21; used from $7)

Common Wealth by Jeffrey D. Sachs: Probably the most informative, in-depth and outlook-changing book you can read on sustainable development.  A must-read if you want to be educated about changing the world.  It is definitely dense, but well worth it.  Sachs knows what he's talking about, after a lifetime of experience using economics to help solve poverty with the U.N. and now as the director of the Earth Institute at Columbia.  (Hardcover at BarnesandNoble: new $20; used from $8.40)

The Live Earth Global Warming Survival Handbook by David de Rothschild: There are too many books you can buy on how to be green, but this one is by far the best.  It's bright, funny, loaded with facts and offers the most effective actions you can take.  My favorite feature is that each action includes a resource, where you can go to find more information.  The other books will show you why; this will show you how, on a small scale.  An Ursuline Environmental Club classic! (Paperback at BarnesandNoble.com: new $5!)